A virtual machine (VM) comprises software that executes on a host computer system to act as if it was a physical machine. A computer system may host multiple virtual machines, each running on a virtual machine monitor (VMM), also referred to as a hypervisor, that controls the sharing of the host's resources among the virtual machines. Typically virtual machines are run to utilize a physical machine's hardware resources more fully than can be done by conventional programs, and/or to run different operating systems on the same physical machine at the same time.
When a virtual machine is created, the virtual machine monitor typically exposes the underlying hardware features, topology and other characteristics to that virtual machine. This allows the virtual machine to fully utilize the capabilities of the platform on which it runs.
There are various reasons why it is sometimes desirable or necessary to migrate a virtual machine from one physical machine to another, without halting execution of that virtual machine (although there is some duration when it is unavailable). Such reasons include load balancing, maintenance, failover and so forth.
However, when a virtual machine is migrated in a heterogeneous computing environment, that is, among computing platforms with different capabilities, a variety of hardware-related and software-related problems can occur. For example, the new platform may not support the instruction set associated with specific processor features that the virtual machine was previously using, resulting in an application or operating system crash. Another problem is when the cache topology differs, e.g., there is a smaller cache line flush size on the new platform, which may result in data corruption issues. Still another problem is that a virtual machine may be optimized to use the Non-Uniform Memory Access (NUMA) topology and/or Non-Uniform I/O Access topology of one physical machine. If one or both of these topologies differs, degraded performance results.
With respect to software, the version of the virtual machine monitor on the new machine may be different from the previous platform's version, resulting in compatibility issues. Also, when a virtual machine is migrated to a differing platform, there may be operating system or application license activation issues.
In sum, in a heterogeneous computer environment, migrating a virtual machine can result in an underutilization of hardware resources, poor performance, system downtime and/or data loss.